Collaborative Research: The Pleistocene Erosion History of Glaciated Alpine Valleys Interrogated by Apatite 4He/3He Thermochronometry

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This research will reconstruct detailed histories of erosion and relief generation at locations within two great coastal mid-latitude mountain ranges, the Coast Mountains of British Columbia and the Southern Alps (Fiordlands region) of New Zealand. Deep and broadly scoured alpine valleys are one of the most spectacular legacies of Quaternary glaciation. However, very little specific information is available about the total magnitudes and the temporal and spatial patterns of erosion and relief development in these valleys. Yet erosion and relief development of these valleys is central to the evolution of the coupled system of erosion, climate, and tectonics that shapes major mountain ranges. Acquiring quantitative information about such valley development over timescales of a few million years and exhumation thicknesses of less than 2 km will be a major contribution toward resolving the question of whether the late Cenozoic transition to glacial climate was accompanied by increased valley incision rates and increased relief generation. This research will be the first systematic application of a very promising new geochemical tool, apatite 4He/3He thermochronometry. This technique is fundamentally different from conventional thermochronometric methods in its sensitivity to uniquely low temperatures and its ability to derive cooling histories from single mineral grains. Results will be examined for connections to the history of global climate change and for characteristic patterns of variation along the longitudinal axes of valley networks. The research will establish the usefulness of a new geochemical technique that has the potential for widespread applications in surface process studies and tectonics. The project will constitute an important part of the research program for a junior PI, and will be one of the first scientific applications of his new noble gas thermochronometry laboratory facility. The proposed work will constitute an important part of a graduate student's doctoral research and training, and will be used as a case study in undergraduate classes.